I recently bought some trans fluid from GM for about 7$ a bottle.
It's no longer named T-IV though...it's branded Dexron-VI.
Either way I just added about 250ml worth...no biggie.
But, in the future, I will go to Toyota for fluids.
When asked, the parts clerk told me that the number change was just to tell old stock from new stock & that the old version.
Oil has a shelf life of about 3-5 years for unopened bottles, depending on the type. 5 seems excessive, so I usually try to get my oil from reliable big stores that have big turnover as opposed to smaller shops. Once opened, I try to use it up within the year.